The present invention pertains to the field of telecommunications, including the field of mobile phone technology. More particularly, the present invention pertains to low power radio frequency communication used for short-distance communication.
Recently, developments in technology have made possible the use of communication devices provided on small electronic chips that can be installed in host devices (such as a personal computer, headset, printer, modem, cellular telephone, or personal digital assistant), allowing the host devices to communicate with each other over short distances, typically from 10cm to 100m, thus making possible wireless communication between the host devices. Such communication is called low power radio frequency (LPRF) communication. One version of this technology is as specified in xe2x80x9cSpecification of the Bluetooth(trademark) System,xe2x80x9d available at http://www.bluetooth.com on the Internet. xe2x80x9cBluetoothxe2x80x9d is a technology trademark owned by Telefonaktiebolaget LM Ericsson.
Bluetooth(trademark) operates in the unlicensed Industry-Scientific-Medicine (ISM) radio frequency (RF) band at 2.4GHz. A frequency hop transceiver is applied to combat interference and fading. A shaped, binary FM modulation is applied to minimize transceiver complexity. The symbol rate is 1 Ms/s. A slotted channel is applied with a nominal slot length of 625 ms. For full duplex transmission, a Time-Division Duplex (TDD) scheme is used. On the channel, information is exchanged through packets. Each packet is transmitted at a different hop frequency, i.e. on a different RF channel. A packet nominally covers a single slot, but can be extended to cover up to five slots.
The Bluetooth(trademark) protocol uses a combination of circuit and packet switching. Slots can be reserved for synchronous packets. Bluetooth(trademark) can support an asynchronous data channel, up to three simultaneous synchronous voice channels, or a channel which simultaneously supports asynchronous data and synchronous voice. Each voice channel supports a 64 kb/s synchronous (voice) channel in each direction. The asynchronous channel can support maximal 721 kb/s asymmetric (and still up to 57.6 kb/s in the return direction), or 432.6 kb/s symmetric.
Referring to FIG. 1, a Bluetooth(trademark) device 14 is shown embedded in a host Bluetooth(trademark) device 10 communicating with another Bluetooth(trademark) host device 16. The Bluetooth(trademark) device 14 consists of a radio unit 11, a link control unit 12, and a support and host interface unit for link management and host interface functions with a host I/O device 15. The Bluetooth(trademark) link control unit 12 carries out the baseband protocols and other low-level link routines. Link layer messages for link set-up and control are defined in a Link Manager Protocol.
The Bluetooth(trademark) system provides a point-to-point connection (only two Bluetooth(trademark) units involved), or a point-to-multipoint connection. In the point-to-multipoint connection, a channel is shared among several Bluetooth(trademark) units. Two or more units sharing a channel form a piconet.
One Bluetooth(trademark) unit, the unit initiating a communication, acts as master of the piconet formed by the sharing of a channel, whereas the other units act as slaves. Up to seven slaves can be active in the piconet. Referring now to FIG. 2, piconets 21-25 are shown, each consisting of a master 21a-25a and one or more slaves 21b-25b and 25c. 
In addition to the up to seven slaves that can be active in a piconet, many more slaves can remain locked to the piconet master in a so-called parked state. These parked slaves cannot be active on the channel, but remain synchronized to the master. Both for active and parked slaves, the channel access is controlled by the master. Multiple piconets with overlapping coverage areas form a scatternet.
Still referring to FIG. 2, each piconet 21-25 can only have a single master 21a-25a. However, slaves 25c can participate in different piconets on a time-division multiplex basis. In addition, a master 25a in one piconet 25 can be a slave in another piconet 23. The piconets are neither time nor frequency synchronized. Each piconet has its own hopping channel.
Although the 2.4 GHz ISM is globally available, the exact location within the ISM band where Bluetooth(trademark) operates may differ by country. In addition, the width of the Bluetooth(trademark) band may vary by country. In the U.S. and Europe, a bandwidth of 83.5 MHz is available; in this band, 79 RF channels spaced 1 MHz apart are defined. In Japan, Spain, and France, a smaller band is available; in this band, 23 RF channels spaced 1 MHz apart are defined.
As indicated above, a logical channel is a pseudo-random (frequency) hopping sequence of slots, hopping through the 79 or 23 physical RF channels. The hopping sequence is unique for a piconet and is determined by the LPRF device address of the master; the phase in the hopping sequence is determined by the LPRF clock of the master. The channel is divided into time slots where each slot corresponds to an RF hop frequency. Consecutive hops correspond to different RF hop frequencies. The nominal hop rate is 1600 hops/s for a Bluetooth(trademark) unit. All LPRF units participating in a piconet are time and hop synchronized to the channel on which they are communicating.
Because all countries today do not dedicate the same RF band for Bluetooth(trademark) communication (or LPRF communication generally), and because the RF band dedicated in some countries is used by the military or government in some other countries, there is a need for a protocol by which a Bluetooth(trademark) device, or other, similar LPRF device, can determine which of the different dedicated RF bands to use. In order to do this, since which band to use is known once it is learned in which country the Bluetooth(trademark) device or similar device is operating, what is needed is a protocol by which a Bluetooth(trademark) device, or an LPRF device generally, can ascertain in what country it is located.
A method, to be performed by a low power radio frequency (LPRF) device, and corresponding apparatus, for determining in what radio frequency (RF) band to communicate, if at all, with another LPRF device, the LPRF band to be determined based on the country where the LPRF device is being used by resorting to information indicating the location and width of the LPRF band for a plurality of countries, the method comprising the steps of, and the apparatus including corresponding means for: acquiring clues from at least one source from among different kinds of sources and from among at least one of different individual sources of each particular kind, the clues consisting of at least one country code indicating one particular country; applying a likely determination algorithm to attempt to determine a likely country based on the clues acquired and a predetermined threshold; attempting to establish a link with the other LPRF device by providing a link setup signal, in a globally available LPRF service band, including, as a self-signaled country code, the likely country code, and receiving from the other LPRF device a corresponding link setup signal; deciding whether the country code signaled by the other LPRF device corresponds to the same RF band as does the self-signaled country code, and so deciding whether there is an agreed-on country code, and if so providing a signal indicating that the link setup is to be completed for communication on the band corresponding to the agreed-on country code, or else repeating the method starting from the acquiring clues step, or, in the apparatus, for signaling the means for acquiring clues to again acquire clues.
In a further aspect of the invention, the different kinds of sources include: the LPRF device itself, which has a country code embedded in it; a cellular signal that provides a country as part of a system information frame, such as GSM; and further, nearby LPRF devices, which periodically transmit a country code on a globally available LPRF service band.
In a still further aspect of the invention, the likely country code is determined based on summing weights associated with each indicated country code, the weights predetermined based on the kind of clue.
In yet a still further aspect of the invention, if a likely country is not determined by applying the likely determination algorithm, querying a user for a country code, and in establishing a link with the other LPRF device, instead of using a likely country code, using the user-provided country code.